Modern electronic components utilize numerous integrated circuits. These integrated circuits can often be electrically connected to each other or to other electronic components. One method of connecting integrated circuits to electronic components utilizes an area array electronic package, such as a ball-grid array (BGA) package or a flip-chip package. With BGA packages, various input and output ports of an integrated circuit are typically connected by wire bonds to contact pads of a package substrate of the BGA package. Solder contacts formed on the contact pads of the BGA package are used to complete the connection to another electronic component, such as a printed circuit board (PCB).
Integrated circuits are also connected to electronic components through a flip-chip electronic package design. The flip-chip electronic package is similar to the BGA package in that solder contacts formed on contact pads of a package substrate are used to make a connection with other electronic components, such as a PCB. Solder contacts are also used in a flip-chip design to attach the input and output ports of a package substrate to the contact pads of the integrated circuit. Therefore, flip-chip packages do not require wire bonds. The solder contacts used to connect the input and output pads of the package substrate to the integrated circuit may be formed on the face of integrated circuits as they reside on semiconductor wafers before being sawed into individual dies.
Solder contacts can be formed using methods, such as printing of solder paste through a stencil or mask, electroplating, evaporation, and mechanical transfer of preformed solder ball or spheres. While electroplating, printing of solder paste through a stencil or mask, and evaporation techniques have been typically utilized for forming solder contacts on wafers and integrated circuits, BGA and chip-scale packages (CSP) have commonly utilized printing of solder paste and mechanical transfer of preformed solder balls to form solder contacts.
Transfer of preformed solder balls has been customarily achieved, by means of vacuum chucks or machined templates. Other methods for transferring preformed solder balls, can include arranging an array of solder balls on the tacky surface of a pressure sensitive tape, aligning the tape and solder balls over the contact pad, and thermally reflowing the solder balls.
Prior to attaching the solder balls to contact pads, solder flux can be applied to either the contact pad and/or the solder balls to facilitate the removal of any oxides or other layers of contamination that may prevent a good solder ball to contact pad adhesion. The solder flux also adheres the solder balls to the contact pads during reflow. Solder fluxes can contain organic based acids for removing the oxides. For conventional area array applications, such as flip-chip packages, PCB, and BGA packages, the solder flux can be applied directly to the contact pads of a substrate by forcing the flux through a screen or stencil. For effective screening oftentimes the flux must be pasty or very viscous. Alternatively, the flux can be applied to the contact pads of a substrate using a stamp system, a ball dip system, or a pin transfer system.